Project Summary Serious skin disorders count among the most devastating health conditions and most difficult treatment challenges. These arise both from genetic diseases and from injuries, such as the often-debilitating long-term suffering of the >500,000 serious burn victims who are hospitalized every year in the US alone. Today's top treatments, including major skin grafts, still struggle to overcome the key natural limitations of human skin's relatively basic repair processes. While these generally restore structural integrity, they often result in extensive scarring that not only causes disfigurement and accompanying psychological trauma, but also significant loss of functionality, including impaired sensitivity and increased susceptibility to infection. The development of more effective skin therapies now stands to benefit greatly from emerging new understanding of the remarkable healing abilities exhibited by naturally regenerative vertebrates. To this end, our longstanding work on the ?axolotl? salamander, the champion among such species, is identifying critical molecules, regulatory pathways and cellular processes underlying scar-free regeneration. Here, we will these address central issues in skin regeneration using cutting edge screening and analysis tools in axolotl. The aim of the project is to: 1) define the exact role of Sall4 in the dermis and epidermis for promoting scar free skin regeneration. 2) harness skin cell transcriptome data to define and functionally elucidate the role of different skin cell populations in regulating scar free regeneration. 3) We will translate our findings of the role of SALL4 in regulating collagen in axolotls into an in vitro model of human skin regeneration and use this new knowledge to attempt to promote scar- free wounding healing in human cells. In summary, these experiments will reveal and characterize key differences between the axolotl's regenerative and the mammal's non-regenerative responses to injury, identifying molecules and pathways required for the former to assess their potential for enhancing the latter. The ultimate aim of these studies is thus to improve quality of life for people with chronic open wounds and dysfunctional scar tissue.